Wave guide rotary joint



y 1952 R. c. HABICH 2,596,398

WAVE GUIDE ROTARY JOINTS Filed Nov. 4, I949 2 SHEETS-SHEET 1 IN V EN TOR. Passer C Has/ow May 13, 1952 R. c. HABICH WAVE GUIDE ROTARY JOINTS 2 SHEETSSHEET 2 Filed Nov. 4, 1949 6 53 I .H n 4 mm 2 5 a N4 m w mH r w N H \\\\\\V\\\\\\\\\ E 7.. C k T \p! loo m h A ow 6 l \\\VAQ L Y B O /u Patented May 13. 1952 WAVE GUIDE ROTARY JOINT Robert C. Habich, Port Washington, N. Y., as-

signor to The Norden Laboratories Corporation, White Plains, N. Y., a corporation of Connecticut Application November 4, 1949, Serial No. 125,602

8 Claims. 1

My invention relates to wave guide rotary joints for the transmission of microwaves through a transmission system capable of angular adjustment.

The rotary joints in microwave guide rotary joints known to the prior art are large and cumbersome and are such as to introduce losses.

One object of my invention is to provide a wave guide rotary joint which is small and which will enable me to maintain good transmission characteristics independent of the relative angular positions of the input and output guides.

Another object of my invention is to provide a wave guide rotary joint in which the shift along the wave guide of the standing wave for different angular positions of the input and output guides is substantially eliminated.

A further object of my invention is to provide a wave guide rotary joint which may be used for high power transmission at conditions of low atmospheric pressure, as for example, in an airplane at high altitudes.

Another object of my invention is to provide a wave guide rotary joint of simple mechanical construction and of small overall size while exhibiting improved electrical properties.

Other and further objects of my invention will appear from the following description.

In general, my invention contemplates the provision of a rotary joint comprising a rectangular input wave guide, a mode transformer for converting a TE1,0 mode existing in the rectangular wave guide to a symmetric circular TMo,1 mode, thus permitting angular rotation, and then retransforming the TMo,1 mode to the rectangular TE1,0 mode in the output rectangular wave guide. I do this by guiding surfaces which will not be excited to produce the undesirable circular TE1,1 mode.

By examining a large number of exciting surfaces I have discovered that a reentrant cone acts as a mode transformer giving a minimum of undesirable reflections and relatively good impedance match for any angular position for the input and output wave guides. We may regard the transmission system from the traveling wave point of view as power being carried down the line by an electromagnetic wave incident upon the load. When this traveling wave encounters some terminating impedance other than the impedance of the line on which it travels. part of the incident wave will be reflected toward the source of power, while the remainder will be absorbed in the terminating impedance. The 1nteraction of the incident and reflected waves on the line input to the terminating impedance will result in standing waves of voltage and current on the input line. In other words, the voltage and current at various points on the line will vary between certain maximum and minimum values depending upon the point of measurement. The magnitude and phase of the standing waves are determined by the load impedance, but the voltage loops always coincide with the current nodes. The extent to which the line and the load are mismatched can be readily determined by measuring the standing wave ratio in the input line. An ideal ratio, of course, will be unity in which no power would be reflected. In my investigations I found that the positive or convex cone, while giving a relatively good mode transformation, gives a high percentage of power reflected. The negative or reentrant cone retained the advantage of good mode transformation and resulted in a construction in which the percentage of power reflected was greatly reduced. An angle between the sides of the cone and its base of greater than 37 gave a standing wave ratio in the input line of about 1.14 and higher. Cones with base angles smaller than 33 gave standing wave ratios in the input line of 1.15 and higher. Cones with. base angles lying between 33 and 37 gave a standing wave ratio between 1.09 and 1.14, representing a small percentage of power reflected. The measurements were made using one frequency having a A of 3.2 cm. Further experiments with frequencies varying between a 7. of 3.17 cm. and a of 3.23 cm. showed comparable results. It was found, however, that at angular positions of 0 and there was an increase in the standing wave ratio. This was thought to be due to the non-symmetrical shape of the transformer since the wave guide entered from one side. I found after considerable work with many expedients that if the wave guide were positioned to fed into the cone itself instead of at the base of the cone two very pronounced effects were obtained in that the effect of angular position of the joint was reduced and it required less depth behind the input wave guide for the joint though the distance between the center lines of the incoming and outgoing wave guides was increased. Using a cone having a 35 base angle, a series of tests was made varying the depth of the recess, that is the overlapping of the upper surface of the inlet wave guide beyond the base of the truncated cone.- When the recess was greater than .045 inch it was found that reflections were again increased to an undesirable degree. When of .24 inch. Into the base of this coneI provided necting the joint to the input wave guide. The

upper duct I4 is rectangular in cross section and discharges into the upper reentrant conical transformer above the base of th frusto-cone overa recess .04. inch deep and .894 inch wide. The

outer transformer comprised a truncatedconehaving the same base angle of 35. The distance between the'center lines of the inlet wave guide and outlet wave guide was .85 inch. The depth of the wave guide was .402 inch. The diameter of the circular wave guide between the reentrant conical frustums was 1.122 inches. 7

'Aspointed out above, the measurements were made using a wave length of 3.2 cm. All of the measurements will vary as a function of Wave length. The angle of the sides ofthe cone'does not vary and remains constant irrespective of wavelength. lhe overlap of the upper surface of the inputwave guide with the base of the mode transformer cone fora wave length of.3.2 cm.

lies between .03 inch and .045 inch. Expressed as a function of wavelength, the .03 inch will be .0238)\. The .045inch Will'be .0357

This wave guide rotary joint wasthen tested in angular positions between and 120 using wave lengths of 3.17,'3.18,.3.-20:and 3.23. and it was found to be quite good, both electrically and mechanically. The'maximum standing wave ratio was 1.12:.02 and the minimum overall inside length was 1.665 inches. The inside length, how- :ever, may be made as long as desired. The corners werethen rounded off to lower the chances of breakdown'or corona discharge.

In the accompanying drawings; which form part of the instantspecification and which are toibe read in conjunction therewith and in which like reference numerals .are used to indicate like :parts in'the various views:

Figure 1 is a sectional elevation ofa wave guide rotary joint showing one embodiment of my invention.

Figure 2 is a plan view viewed along the line 2- 2 of Figure 1.

Figure 3 is a side elevation viewed along the line3--'3 of Figurel.

Figure 4- is a sectional view taken along the line 4-4 of. Figure 1.

Figure 5 is av sectional view of a waveguide rotary-joint showing anotherembodiment ofmy invention.

Figure 6i'sa side elevation taken along the line 5-4 of Figure5.

Figure 7 is a sectional View taken along the Figures is a sectional view drawn on an enlarged scale showing the TMc,1 mode in the circular-wave guide between the upper reentrant conicalinput transformer-and the lower reentrant conical output transformer.

.ings, thereentrant sectionv of my, joint comprises an upper body. member l0 made of an aluminum alloyor thelike. Aflange l2 isprovided for conlapping .04 inch. The interior side l5 of the cone makes an angle of 35 with the base of the cone.

The internal diameter of the cylinder below the cone is 1.122 inches. The height of the internal dimension of the rectangular waveguide I4 is .04 inch. The width of the rectangular wave guide I4 is .90 inch. Integral with the body member I0 I provide a flange l6 and a stud I8. The

..flange i6 is formed with a rabbet into which the cylindrical end 20 of the lower body member 22 is adapted to fit. The upper interior cylindrical portion of the lower body member merges into a reentrant conical transformer similar to the upper transformer. The S-shaped duct 24 is rectangular in cross section and comprises the output waveguide. A flange 26 is provided for connecting the outputduct 24 to the output wave guide of rectangular cross section] An upper flange .28 is formed integrally with .the body member 22. A brass ring 30 is adapted toseat upon the flange 28. An upper brass ring ,32 is secured .to the lower brass ring 30 .by means'of machinefscrews 34. The outer race 36 of a ball bearing. rests on the ring 30; the inner race.38 of r a ballbearing rests .upon the ,flange' I6. ,Ball bearings Mare provided between the races. vA bracket 42 is secured to the ring .32 by ap urality ,ofmachine screws 44. The upperend of the bracket carries a ,ball bearing 46 coacting with the-stud l8 andis adapted to prevent the two. portions of the joint from separating along theaxisof' rotation. In th form of my .joint shown in Figures 1 to .4 the axis of the. input wave guide-forms an angle of .90" with-the axis of. theoutput wave guide and .the input waveguide may be rotated relatively to the output wave guide around the axis v of the output waveguide through an angle of approximately 120.on each side of the center line.

' "Referring now to Figure ,5, I have shown an- 7 otherenibodiment of my, invention in whichthe axis of the output waveguide ,and the axisof waveguide M, .the stu'dl8 and the;flange IS.

The output member'50,.however, is generallysimilar to the input member and has an output wave.

. duct 52 rectangular in cross section terminating in-flangeji4 adapted to'be secured to the output wave-guide. .A'flange 55 is adapted to support a lower brassring 58 which is adapted to be secured 'to the upper brass'ring 1.32 by means of machine' screws '34. The outer race 30 issupported by the-ring 5'8while the inner race38 .contacts the flange l6. Ball bearings 40 are provided between the inner and outer races. 7

The structure. of the modification shown in Figures 5,6 and 7 isgenerally similar "to' that shown in Figures 1 to eexcept that theaxis-of the output wave ductis parallel-to the plane in which relative rotation between the input and output wave ducts takes place. It .willbe .observed that the interior upper cylindrical portion 5110f the lower portion of the joint merges. with th j lower conical reentranttransformer. The

side 49 of the. lower:transformerjforms an, angle of with. the base ofthe cone. Theside t5 of the upper transformer. forms an angleof 35 with. the .baseof the cone. .The gap between the .lower end ll of the upper cylindrical portionand the upper end 39 of the lower cylindrical portion which together form the cylindrical wave guide between the transformers is .02 inch.

Referring now to Figure 9 which shows the TE1,0 mode in the upper rectangular wave guide and the output wave guide, the lines 66 represent the electrical field and the horizontal dotted lines GI represent the magnetic field.

This mode is transformed by the transformer into the TMD,1 mode in the circular wave guide between the transformers. This mode is shown in Figure 8, in which the radial lines 76 represent the electrical field and the broken line circles H represent the magnetic field. This mode is transformed by the output transformer back to the TE1,0 mode shown in Figure 9.

It will be seen that I have accomplished the objects of my invention.

I have provided a wave guide rotary joint which is small in physical size but which will enable me to maintain good transmission characteristics independently of the relative angular positions of the input and output wave guides. I have provided a wave guide rotary joint in which the shift along the wave guide of the standing wave for different angular positions of the input and output guides is substantially eliminated. I have provided a wave guide rotary joint by which I may transmit high power at conditions of low atmospheric pressure and which is of simple mechanical construction and small overall size, and which at the same time exhibits improved electrical properties.

It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to the specific details shown and described.

Having thus described my invention, what I claim is:

1. A microwave guide rotary joint including in combination an input wave guide of rectangular cross-sectional shape, a transmission wave guide of circular cross-sectional shape having its axis disposed at right angles to the axis of the input Wave guide, an output Wave guide of rectangular cross-sectional shape, an input mode transformer positioned in the transmission system between the input wave guide and the circular wave guide, an output mode transformer positioned between the circular wave guide and the output wave guide, each of the mode transformers being formed with an exciting surface lying along the interior side of a cone converging in a directio away from an intermediate plane transverse to the axis of the circular wave guide and means for permitting relative rotation of an upper portion of the circular wave guide with respect to a lower portion thereof.

2. A microwave guide rotary joint as in claim 1, in which the input mode transformer is adapted to convert a rectangular TE1,0 mode into a symmetric circular Til/10,1 mode and the output mode transformer is adapted to convert a symmetric circular 'IMo,1 mode into a rectangular 'IE1,c mode.

3. A microwave guide rotary joint as in claim 1, in which the mode transformers comprise cones whose sides form an angle with the bases of the cones of between 33 and 37.

4. A microwave guide rotary joint as in claim 1, in which the upper surface of the input wave guide overlaps the base of the conical input mode transformer by an amount between 0238a and .0357A.

5. A microwave guide rotary joint as in claim 1, in which the lower surface of the output wave guide overlaps the base of the conical output mode transformer by an amount between .0238 and .0357A.

6. A microwave guide rotary joint as in claim 1, in which the mode transformers comprise truncated cones.

7. A microwave guide rotary joint as in claim 1, in which said circular wave guide comprises an upper portion formed integrally with the upper mode transformer and the lower portion formed integrally with the lower mode transformer, a flange formed about the lower end of the upper cylindrical wave guide portion, a flange formed about the upper end of the lower cylindrical wave guide portion, a bearing positioned between said flanges and means for holding said flanges together.

8. A microwave guide rotary joint as in claim 1, in which said output Wave guide is formed with an S-bend and the axis of the terminating portion of said bend extends at an angle of substantially to the axis of the input wave guide.

ROBERT C. HABICH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,484,822 Gould Oct. 18, 1949 2,513,205 Roberts June 27, 1950 

